Continuous centrifuge of the type having an underflow return circuit



Jan. 13, 1953 J. G.'GLASSON 2,625,321

CONTINUOUS CENTRIFUGE OF THE TYPE HAVING AN UNDERFLOW RETURN CIRCUIT Filed March 7, 1949 2 SHEETS-SHEET 1 FIIEI J IN V EN TOR. John G G/a 55 on qrromyzys Jan. 13, 1953 J sso 2,625,321

CONTINUOUS CENTRIFUCE OF THE TYPE HAVING I AN UNDERFLOW RETURN CIRCUIT Filed March '7, 1949 2 SHEETS-SHEET 2 I IN V EN TOR.

John G. G/asson /4 TTOIQ/VEYS Patented Jan. 13, 1953 CONTINUOUS CENTRIFUGE OF THE TYPE HAVING AN UNDERFLOW RETURN CIR- CUIT John G. Glasson, San Anselmo, Calif., assignor to Merco Centrifugal 00., San Francisco, Calif., a. corporation of California Application March 7, 1949, Serial N 0. 80,077

4 Claims.

This invention relates generally to centrifuges of the type adapted for the continuous separation and discharge of separated underflow and overflow fractions from a feed material containing suspended solids.

Continuous centrifuges of the type disclosed in Patents 1,923,454, 1,847,751 and 2,060,236 utilize a so-called return circuit by means of which a major part of the centrifugally separated underflow is continuously returned to the centrifuge rotor. A commercial machine of this character makes use of a housing which generally encloses the rotor, and which is formed to provide volutes or like means for receiving the underflow and overflow materials. The rotor is provided with a lower conical shaped impeller portion which has an axially disposed opening faced downwardly, and which is adapted to receive the returned underflow material. A nozzle is provided in the lower end of the housing in alignment with the opening in the impeller, and this nozzle is connected by piping to the underfiow volute. Thus a return circuit is formed whereby a large part of the under-flow material is continuously jetted upwardly into the impeller, and is forced outwardly by the impeller into the outer peripheral portion of the separating chamberof the rotor. In some instances the return circuit may include one or more tanks or vent boxes, and a gravity head or pump can be provided for supplying the returned material to the nozzle at a substantially constant pressure.

' One problem which has been encountered in the operation of such machines is that some material spills from the rotor, and tends to collect in thelower part of the housing. Part'of this spill may occur from the peripheral underflow nozzles, which may not deliver all of the discharging underflow material into the underfiow volute. Some additional spill may occur as back splash from the underflow volute. In addition some spill may occur from the upwardly directed jet of returned material as it discharges into the impeller, and some material may be discharged from the lower end or lip of the impeller. Irrespective of the source or sources of spill, it interferes with proper operation of the machine. It tends to cause surges in the operation of the machine, particularly where sufiicient liquid may collect to momentarily and recurrently submerge the lower end of the impeller. In addition spill tends to increase power consumption and may cause contamination of the separated fractions. It has been unsatisfactory to attempt continuous drainage of spill from the lower end of the housing, as by means of a drain pipe. When such a drain connection is used a considerable amount of spill tends to remain in the housing, and that part which can be drained 01f requires special handling for returning to the system.

As disclosed in copending application Serial No. 753,301, filed June 7, 1947, now Patent #2,559,453 it has been proposed to provide aspirating means for the purpose of merging the collected material with the upwardly directed jet of return material. It has been found however that such aspirating means does not always return the spilled material as efficiently as desired, and in some instances, particularly for the higher speeds of rotation, can be relatively ineffectual. It is an object of the present invention to pro vide an improvement in centrifugal machines of the above character, which will enable efilcient return of the spilled material into the impeller of the rotor, and which will function under all con 'ditions of operation.

Another object of the invention is to provide a centrifuge of the above character having improved means which will insure proper collection and flow of spilled material to aspirating means located at the lower end of the rotor housing.

Additional objects and features of the invention will appear from the following description in which the preferred embodiments have been set forth in detail in conjunction with the accom p ying drawing.

Referring to the drawing: 7

Figure 1 is a side elevational view partly in section illustrating a centrifuge incorporating the present invention.

Figure 2 is an enlarged detail in section showing the lower portion of the machine.

Figure 3 is a diagrammatic plan view illustrating one type of return circuit.

Figure 4 is a fragmentary plan view of the lower part of the centrifuge housing and illustrating one type of vane construction.

Figure 5 is an enlarged cross-sectional detail taken along the line 5-5 of Figure 4.

The centrifuge illustrated in Figure l of the drawing consists generally of the rotor l0 carried by the vertical shaft I, and disposed within the stationary housing l2. As will be presently explained the rotor is provided with various passages, including a passage for the inflow of fluid feed material, a passage for discharge of lighter centrifugally separated overflow, and a passage for introducing a supplemental fluid material which is preferably heavier centrifugally separated discharge material or underflow.

The rotor shaft H is connected by coupling it to the vertical shaft hi of a bearing assembly it. The housing 62 can be conveniently formed of a plurality of separable sections l2c, (2b and 120. Section 52a forms a vciutc chamber ii for receiving centriiugally separated overflow, and section 1% is formed to provide the volute chamber 22 which receives underfiow or heavier separated material.

The body of the rotor can likewise be made of number of separable parts, including in this instance the main part Ida, and the upper and lower conical shaped parts lllb and lilo. The part Hla. has an inner structure 23 which is attached to the lower end of the rotor shaft 1 I. Parts Illa and 19b are retained together by suitable means such as the expansible clamping ring 24. Within the separating chamber of the rotor there is a group or stack of separating discs 21 such as are commonly used in centrifuges. Mounted within the outer peripheral wall 23 of the main body part Ida are the circumferentially spaced underflow nozzles 28, each of which is provided with a discharge orifice directed backwardly with respect to the direction of rotation. The annular periphery 28 of the rotor body We is accommodated within a diverging portion 3| or throat ring of the housing part 1222.

The lower portion We of the rotor forms an impeller for the return of centrifugally separated underfiow material back into the rotor. Thus the lower end of the rotor part 160 is provided with an axially and downwardly faced opening 44. This opening is directly above a nozzle 46 carried by the lower part of the housing, and which as will be presently explained serves to direct a jet or solid stream of the returned underflow material upwardly into the impeller. The opening 44 of the impeller is formed in a ring 4? which is removably mounted on the lower end of the rotor part We- Within the impeller the material is acted upon by the radially extending vertical webs or vanes 52, which serve to act upon and impart rotor velocity to the material. The material passing through the spaces between the vanes 52 passes upwardly and outwardly through the passages 53 to the outer annular space 5d which forms a part of or communicates with the main separating chamber 26, and which also communicates with the discharge nozzles 29. The inner walls of passages 53 are defined by the conical shaped member 55, which is upwardly divergent and which is attached to the structure 23.

The lower portion 20 of the housing is conical shaped, and conforms generally to the contouring of the lower part of the rotor. Thus spilled fluid material (in the absence of extraneous forces) tends to collect in the lower part of the housing adjacent the lower end of the rotor.

I make use of means such as disclosed in copending application Serial No. 753,301, filed June '7, 1947, now Patent #2,559,453, to return spilled material from the lower end of the housing into the stream of returned underfiow material. Preferably this means is an aspirating device, which returns the spilled material and merges the same with the upwardly discharging jet issuing from the nozzle 46.

The aspirating means in this instance consists of an annularly contoured member 48, which can be formed of sheet metal, and which is mounted immediately over the nozzle 46. The member 48 includes an upwardly extending conical shaped portion 49, which forms an opening 5| at its upper end of a diameter only slightly larger than the concentric orifice opening 55. Member 48 also has a skirt 50 which extends outwardly, and which is held in fixed position by the screws or bolts 51, in conjunction with the spacers 58. This arrangement forms a passage 59 between the member 48 and the adjacent surface of the nozzle 46. The outer peripheral inlet portion 60 of the passage 59 is adapted to receive spilled material and when the machine is in operation, the jet of material discharging upwardly from the nozzle orifice 55 tends to induce flow through the passage 59 by virtue of an aspirating action, and this serves to draw material through the passage 59 from the inlet 60, and merge this material with the upwardly discharging jet.

As has been previously stated, aspirating means such as described above may not always be as effective as desired, and in some instances it will be relatively ineffectual, particularly where the rotor is driven at relatively high speed. I have discovered that this is due to a tendency of the spilled material to swirl about the vertical axis of the housing in a region extending outwardly from the inlet 80. Such swirling movement interferes with the desired even flow of the spilled and collected material into the passage 59, and thus the aspirating device does not have an opportunity to properly function. The swirling movement is attributed largely to swirling turbulent air within the lower part of the housing, which in turn is due to the high speed of rotation of the rotor.

I have found that it is possible to secure efiective and efiicient return of spilled material by providing the lower part of the housing with a plurality of bailles or vanes 6|. In that form of the invention illustrated in Figures 1 and 2 these vanes are mounted upon the upper wall of the housing portion I20 and they extend substantially the entire height of this housing section. As viewed in plan, the vanes in this instance extend in a substantially radial direction. It is not essential that the vanes be of sufficient length to extend to the upper edge of the housing section iZc. However it is desirable that they extend outwardly and upwardly a substantial distance from points adjacent the passage inlet 60.

In that form of the invention illustrated in Figures 4 and 5, a special form of vane or bafile is employed, in place of the simple upright vanes of Figures 1 and 2. In this instance each vane 62 consists of an upright portion 52a, together with a flange portion 62b. The flange portion extends ln a direction opposite to the direction of rotation of the rotor. As viewed in plan (Figure 4) the vanes 62 are curved so that their upper extremities extend backwardly with respect to the direction of rotation.

Figure 3 illustrates one type of underfiow return circuit for use with the machine. Thus in this instance a pipe 66 is connected tangentially with the underflow volute 22 and also with the lower end of the housing, whereby the pressure of material in the volute 22 causes the material to be discharged upwardly through nozzle 46. Valve controlled pipes 5'! and 58 can serve to draw off underfiow material, and to introduce wash water. As previously stated, the return circuit may include a tank or vent box (see Patent 2,039,605)

When a machine is equipped with baffles or vanes as described above, material spilled into the rotor housing is efiiciently returned to the rotor under all conditions of operation. Ihis is attributed to the fact that swirling of the collected spilled material is prevented by the vanes, and also because the vanes tend to break up swirling air currents between the lower part of the rotor, and the adjacent walls of the housing. Collected spilled material therefore flows continuously down the walls of the housing, and into the inlet passage 58, and the quantity of spilled material within the housing at any one time is maintained at a minimum. A centrifuge constructed in accordance with my invention is relatively free of surging, because the spilled material. is collected and returned to the rotor at a substantially constant rate. In other words there is no unevenness to the return of spilled material,

such as is conducive to surging in the machine, I=

and which tends to upset delicate separating conditions.

I claim:

1. In a centrifuge construction, a vertically disposed rotor adapted to receive feed material and arranged for separate discharge of centriiugally separated underfiow and overflow fractions, a housing serving to enclose the rotor, means forming part of the housing for separately collecting and removing overflow and underflow fractions being discharged from the rotor, an impeller forming the lower part of the rotor and having a lower opening faced downwardly, said housing including a lower portion generally embracing said impeller and formed to receive materials spilled from the rotor and to collect such spilled material in the lower end thereof, the space between said lower :portion of the housing and said impeller forming a windage zone during operation of the machine, means for delivering a portion of the underfiow material as an upwardly directed jet into the impeller and through said downwardly faced opening, a bafile means mounted in the walls of the lower part of the housing in said windage zone and. serving to minimize swirl of spilled material, and means disposed below the lowe end of the rotor for continuously conducting collected and spilled material from the lower portion of the housing into the stream of underflow material being discharged into the impeller.

2. In a centrifuge construction, a vertically disposed rotor adapted to receive feed material and arranged for separate discharge of centrifugally separated underflow and overflow fractions, a

housing serving to enclose the rotor, means forming a part of the housing for separately collecting and removing overflow and underfiow fractions being discharged from the rotor, an impeller forming the lower part of the rotor and having a lower axial opening faced downwardly, said housing including a lower portion generally embracing said impeller and formed to receive material spilled from the rotor and to collect such spilled material in the lower end thereof, the space between said lower portion of the housing and said impeller forming a windage zone during operation of the machine, means for delivering a portion of the underfiow as an upwardly directed jet into the impeller and through said downwardly faced opening, whereby underflow material is continuously returned to the rotor, aspirating means disposed at the lower end of the housing and serving to cause spilled material collected in the lower part of the housing to be merged with the upwardly discharging jet of underfiow material. said last means including means forming an annular conducting passage surrounding the jet and extending inwardly and upwardly toward the same, there being a vertically extending space between said path and the lower end of the rotor, and bailie means for minimizing swirl in said windage zone and swirl of spilled material in the lower portion of the housing, said baflie means comprising vanes mounted on the walls of the lower part of the housing and disposed in said windage zone.

3. In a centrifuge construction, a vertically disposed rotor adapted to receive feed material and arranged for separate discharge of centrifugally separated underflow and overflow fractions, a housing serving to enclose the rotor, means for separately collecting and removing overflow and underflow fractions being discharged from the rotor, an impeller forming the lower part of the rotor and having a lower axial opening faced downwardly. said housing including a lower portion generally embracing said impeller and formed to receive material spilled from the rotor and to collect such spilled material in the lower end thereof, the space between said lower portion of the housing and said impeller forming a windage zone during operation of the machine, means for delivering a portion of the underflow as an upwardly directed jet into the impelle and through said downwardly faced opening, whereby underflow material is continuously returned to the rotor, said last means including a nozzle disposed at the lower end of the housing, aspirating means disposed adjacent said nozzle and serving to cause spilled material collecting in the lower part of the housing to be merged with the jet of underflow material being discharged into the impeller, said aspirating means including means forming an annular conducting passage surrounding the nozzle and extending inwardly and upwardly toward the jet, said passage having its upper side defined by a stationary member disposed below the rotor and spaced from the same, a plurality of vanes mounted upon the walls of the lower portion of the housing and in said windage zone, said vanes being distributed about the axis of the rotor and extending upwardly and outwardly relative to the rotor axis, the inner ends of said vanes terminating adjacent the perimeter of said member, said vanes serving to reduce swirl of windage and to prevent swirl of spilled material in said housing and to direct the same into said passage.

4. A centrifuge construction as in claim 3 in which the vanes, as viewed in plan, are curved whereby their outer portions bend toward a direction opposite to the direction of rotation of the rotor.

JOHN G. GLASSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 699,217 McCornack May 6, 1902 706,033 McCornacl: Aug. 5, 1902 1,847,751 Coe Mar. 1, 1932 1,923,454 Peltzer et a1 Aug. 22, 1933 2,013,668 Peltzer et al Sept. 10, 1935 2,138,468 Ayres Nov. 29, 1938 2,525,629 Zimmerman et a1. Oct. 10, 1950 

